Sharing of power level information to support optical communications

ABSTRACT

In an optical communication network, optical communication nodes exchange information detailing power level variations to support management and administration of optical communications. This exchange of information permits nodes to determine aggregate power level variations over light paths to support operations such as selection from available light paths and configuration of optical communication characteristics.

TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates generally to optical communicationnetworks and, more particularly, to power level management in opticalnetworks.

BACKGROUND OF THE INVENTION

[0002] In typical synchronous optical network (SONET) systems, powerlevel management is performed during the installation of a network,often manually, and then re-optimized with the addition or deletion ofconnections in the network. By measuring the channel power levels andoptical signal-to-noise ratios at different points in the network, powerlevels at transmitters may be adjusted according to algorithms,improving the performance of the connections with smaller opticalsignal-to-noise at the cost of those connections with higher opticalsignal-to-noise. In addition, amplifiers often operate in an automaticlevel control (ALC) mode to minimize the impact of changes in span powerlosses. In this mode, changes in one channel's power level can influenceanother channel's power levels, thus complicating attempts to managepower levels. Because changes in particular power level parameters canaffect the settings of other power levels, administrators often employtime consuming, iterative processes to achieve power level balancing.

SUMMARY OF THE INVENTION

[0003] In accordance with the present invention, techniques for powerlevel management in optical networks are provided.

[0004] According to a particular embodiment, a method for power levelmanagement of optical communications receives a request to establish acommunication channel with a remote optical node and determines aplurality of light paths to the remote optical node. For each of thelight paths, the method determines a next node for the light path to theremote optical node, determines add power level variation for the lightpath, generates a path setup message identifying the light path and theadd power variation, and communicates the path setup message to the nextnode.

[0005] According to a another embodiment, a method for power levelmanagement of optical communications receives a path setup messageidentifying a light path between an add node and a drop node, the pathsetup message comprising a power level variation value, and determineswhether a channel for the light path to a next node in the light path isavailable. If the channel is available, the method determines throughpower level variation for the light path, adds the through power levelvariation to the power level variation value in the path setup message,and communicates the path setup message to the next node in the lightpath.

[0006] According to a another embodiment, a method for power levelmanagement of optical communications receives a plurality of path setupmessages corresponding to a plurality of light paths from a remoteoptical node, each of the path setup messages identifying one of thelight paths and indicating a power level variation value for theidentified light path. For each of the path setup messages, the methoddetermines drop power level variation for the light path identified inthe path setup message, adds the drop power level variation to the powerlevel variation value in the path setup message to obtain an aggregatepower level variation for the identified light path, generates a setupreply message indicating the identified light path and the aggregatepower level variation for the light path, and communicates the setupreply message to the remote optical node.

[0007] According to a another embodiment, a method for protectionswitching in an optical network detects failure of a light path,determines a protection light path, determines drop power levelvariation for the protection light path, generates a protection switchmessage identifying the protection light path and the drop power levelvariation, and communicates the protection switch message to a previousnode on the protection light path.

[0008] Embodiments of the invention provide various technicaladvantages. Using these techniques, networks may implement power levelmanagement more quickly than compared to previous techniques. This speedof operation provides a number of advantages. For example, protectionswitching may require rapid response in the event of a severed link.With the disclosed techniques, power level management during protectionswitching, or even link restoration, can be implemented. Moreover, thepotential speed of these techniques may also support emerging opticaltechnologies, such as dynamically routed mesh networks.

[0009] In addition, these techniques can be implemented along with otherand/or existing power level management techniques. For example, thesetechniques may be used to provide quick power level management, withother techniques, such as iterative power level adjustments, used forfine-tuning of power level adjustments.

[0010] Other technical advantages of the present invention will bereadily apparent to one skilled in the art from the following figures,descriptions, and claims. Moreover, while specific advantages have beenenumerated above, various embodiments may include all, some, or none ofthe enumerated advantages.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] For a more complete understanding of the present invention andits advantages, reference is now made to the following description,taken in conjunction with the accompanying drawings, in which:

[0012]FIG. 1 illustrates an optical communication system having nodesthat perform power level management in accordance with variousembodiments of the present invention;

[0013]FIG. 2 illustrates a node from the optical communication systemoperable to perform power level management in accordance with variousembodiments of the present invention;

[0014]FIG. 3 illustrates a particular example of power level managementin the optical communication system;

[0015]FIG. 4 is a flowchart illustrating a method for performing powerlevel management at an add node for a light path;

[0016]FIG. 5 is a flowchart illustrating a method for performing powerlevel management at an intermediate node of a light path;

[0017]FIG. 6 is a flowchart illustrating a method for performing powerlevel management at a drop node of a light path; and

[0018]FIG. 7 is a flowchart illustrating a method for performing powerlevel management during protection switching.

DETAILED DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 illustrates an optical communication system, indicatedgenerally at 10, that includes optical nodes 12 forming an opticalnetwork 14, which provides for the transportation of information betweenvarious elements such as communications devices 16. In general, nodes 12communicate to determine aggregate power level variations on light pathsto provide power level management for the light paths. Morespecifically, a selected node 12 (add node) attempting to establish alight path to another node 12 (drop node) may communicate with variousnodes 12 to determine power level variations on one or more light pathsfrom the add node to the drop node. The add node may use these lightpath power level variations to select and configure a light path to thedrop node through network 14.

[0020] Network 14 represents any suitable collection and arrangement ofelements providing for the communication of information in opticaltransmissions. This may include any appropriate electrical and opticalinterconnections to support the establishment of light paths forcommunication of information using circuit switched and/or packet basedprotocols. Each light path represents a communication channel spanningbetween two or more nodes 12. For example, according to particularembodiments, nodes 12 communicate information using wave-length divisionmultiplexed (WDM) protocols. Thus, in certain embodiments, two adjacentnodes 12 may potentially be linked by multiple available light paths,such as a light path on each channel.

[0021] Nodes 12 represent hardware, including suitable controllinglogic, supporting the communication of information in opticaltransmissions. For example, nodes 12 may provide add drop multiplexer(ADM) functionality to add, propagate, and drop optical signalstransmitted on light paths. Each node 12 links using optical fibers toother nodes 12 in network 14 and potentially to other communicationsequipment, such as devices 16. In addition, each device 12 may link withother communications equipment, such as devices 12, using electricalcommunication channels to exchange management messages. For example,nodes 12 may exchange multi-protocol label switching (MPLS) messagesusing electrical communication channels. However, the system 10contemplates nodes 12 using any suitable optical, electrical, or othercommunication links to support communication of management messages forthe administration of optical communication links.

[0022] In the example illustrated, nodes 12 provide multiples routes(each potentially having multiple light paths) for opticallytransmitting information from a first device 16 (device A) to a seconddevice 16 (device B). However, the example provided illustrates onlyselected elements and connections, and system 10 contemplates includingany suitable elements providing connectivity between any number and typeof communications equipment. Devices 16 represent any suitable equipmentfor the transmission and receipt of communications across opticalnetwork 14. For example, devices 16 may include gateways, switches,routers, and/or any other suitable communications equipment locatedwithin public or private networks.

[0023] In operation, nodes 12 provide power level management byexchanging power variation information to determine aggregate powerlevel variations across light paths. To enable rapid calculation ofpower level variations for light paths, each node 12 maintains powerlevel information indicating power level variations for each potentialpath (add, drop, and through) for node 12. For example, consider node 12having sixty channels for optically transmitting information. Node 12will maintain power level variations for adding, dropping, and passingthrough optical signals at a wavelength for each channel. Thus, for thisexample, node 12 maintains one hundred eighty values for power levelvariations (sixty for adding signals, sixty for dropping signals, andsixty for passing through signals). In addition, nodes 12 may maintaintransmission power level variations measuring the variations in powercaused by the transmission of optical signals across optical fibers. Forexample, each node 12 can measure and/or maintain information indicatingthe amount of power level variation resulting as optical signalspropagate along optical fibers from adjacent nodes 12.

[0024] When establishing a link between an add mode and a drop node,nodes 12 communicate to determine aggregate power level variations alongone or more light paths between the add node and the drop node. Anaggregate power level variation indicates the sum of the add power levelvariation at the add node, the drop power level variation at the dropnode, and through power level variations at each of the intermediatenodes in a light path. Based upon the aggregate power level variations,the add node selects a light path and configures to provide effectivecommunications on the selected light path. For example, the add node mayselect the light path with an aggregate power level variation closest toa target and then set variable attenuation for the wavelength of theselected light path to a value appropriate to compensate for thedetermined aggregate power level variation.

[0025] For example, consider device 16 labeled A (device A) withinformation for communication to device 16 labeled B (device B). Tocommunicate this information, network 14 may establish a link betweennode 12 labeled A (node A) and node 12 labeled B (node B). Thus, in thisexample, node A functions as an add node and node B functions as a dropnode for transmissions. Node A, upon receiving an appropriate indicationto establish a link with node B, such as a request from device A,initiates a process to determine power level variations along one ormore light paths between node A and node B. To initiate the process,node A may first identify available light paths to adjacent nodes 12 onroutes to node B. For example, node A may determine currently availablechannels to node C, node D, and node E. For each identified light path,node A determines the add power level variation, encodes this value intoa path setup message, and communicates the setup message to the nextnode 12 on the light path.

[0026] For example, for each available wavelength between node A andnode C, node A may determine the add power level variation for thewavelength, encode the value within a path setup message, andcommunicate the path setup message to node C. Node A may perform similaroperations for available wavelengths to node D and node E. Thus, node Amay communicate setup messages for multiple wavelengths to each of nodeC, node D, and node E. However, system 10 contemplates node A combiningor separating the setup messages into one or more messages communicatedto each of node C, node D, and node E. For example, node A maycommunicate a setup message for each available wavelength to Node C,with each setup message indicating the add power level variation withinnode A for the wavelength. Alternatively, node A may combine thisinformation to reduce the number of setup messages communicated, such asby generating a single path setup message indicating each of theavailable wavelengths and, for each wavelength, the add power levelvariation within node A.

[0027] The path setup messages propagate along the paths between node Aand node B, aggregating power level variations along the way. Along alight path, each intermediate node 12 supplements the encoded powerlevel variation in a path setup message with a value for through powerlevel variation. For example, node C receives one or more path setupmessages from node A, with each message identifying a particularwavelength and specifying a power level variation (the specified powerlevel variation at this point reflects only the add power levelvariation of node A at this wavelength). For each path setup message,node C determines whether the indicated wavelength is available to thenext node 12 or nodes 12 in paths to node B. If so, node C determinesthrough power level variations for the wavelength, adds this value tothe power level variation encoded in the path setup message, andforwards the message to the next node or nodes 12. Therefore, as a setupmessage propagates through network 14, it accumulates power levelvariation information from each traversed node 12.

[0028] Node B thus receives one or more path setup messages identifyingsome or all potential light paths from node A through Network 14. Foreach message identifying a potential light path, node B determines droppower level variation for the identified wavelength and adds this valueto the aggregate power level variation from the path setup message. Thisaggregate power level variation then reflects the total of the add,through, and drop power level variations affecting the light path. NodeB replies to node A indicating the aggregate power level variations foreach of the potential light paths. As with other management messages,nodes 12 may use separate messages for each reply or combine two or morereplies into a single message. Regardless, these replies permit theoriginating node 12 (node A) to select between potential paths based onthe aggregate power level variations for these paths.

[0029] Upon receiving the replies, node A may use any suitabletechniques for selecting between potential paths. According toparticular embodiments, node A selects the potential path having a powerlevel variation closest to a target value. This target may be zero or anon-zero value. For example, power level variations for light paths mayhave a typical or average value for which nodes 12 can be designed toaccommodate. The target value may reflect this “expected” power levelvariation. However, system 10 contemplates nodes 12 using any suitablealgorithms, criteria, and techniques for selecting between potentiallight paths based upon aggregate power level variations.

[0030] Using the aggregate power level variation of the selected lightpath, node A can also adjust its operational characteristics. Forexample, Node A may adjust variable attenuation to accommodate theaggregate power level variation along the selected light path to providean acceptable signal for receipt by node B. However, nodes 12 may havelimited dynamic ranges that permit accommodation for only certainamounts of power level variation. If all of the potential light pathshave an aggregate power level variation that exceeds the capabilities ofthis dynamic range, node A may indicate failure in establishing the linkto node B.

[0031] According to particular embodiments, nodes 12 support protectionswitching using power level management techniques similar to thosedisclosed above. This leverages on the speed of these techniques topermit power level management in protection switching scenarios. In manyoptical systems, specifications dictate speeds at which protectionswitching must occur. For example, an optical system may requireprotection switching to occur in less than 50 milliseconds. According toparticular embodiments, the disclosed techniques permit power levelmanagement and protection switching to occur in less than 50milliseconds and potentially in less than 15 milliseconds. At thesespeeds, optical systems may even incorporate restoration in place ofprotection for severed links. In protection switching, a particularlight path is selected as backup for an active link. If the active linkfails, traffic is switched to the backup. In restoration, a new lightpath is selected from potential light paths on the failure of an activelink. Thus, restoration potentially chooses a more effective linkcompared to protection.

[0032] To provide protection switching, nodes 12 monitor active lightpaths and, in the event of a failure, initiate switching ofcommunications to a new light path. For example, consider acommunications link between node A and node B along a light path routedover intermediate nodes D and G. Further assume a protection light pathis assigned along the route of nodes C, F, and I. While the primarylight path remains active, node B may monitor for failure. To monitornode B may use any suitable techniques to detect failure of the lightpath, such as by detecting the absence of light on the path.

[0033] Given a failure of the preliminary light path, node B initiatesswitchover to the backup light path. To effect the switch to the backuplight path, node B generates a switchover message and communicates themessage to node A along the route of the backup light path. Thus, theswitchover message traverses nodes I, F, and C to reach node A. Togenerate the switchover message, node B determines drop power levelvariation for the wavelength of the backup light path and encodes thisvalue within the switchover message. Then as the switchover messagepropagates to node A, each intermediate node 12 supplements the powerlevel variation information with appropriate values. Thus, nodes I, F,and C each add values for through power level variation at thewavelength specified for the backup light path. Therefore, node A maycalculate the aggregate power level variation for the backup light pathwith the addition of the add power level variation within node A to thepower level variation indicated in the received switchover message.Using this information, node A may configure its operation to provideacceptable signals along the backup light path. For example, asdiscussed above, node A may configure variable attenuation toaccommodate for the aggregate power level variation expected along thebackup light path.

[0034] In addition or as an alternative to providing protectionswitching, nodes 12 may support restoration of communications links uponfailure of a light path. For example, consider the previous descriptionof a failure along a primary light path from node A to node B traversinga path through nodes D and G. Upon detecting a failure of the primarylight path, node B may initiate a restoration process using messagingsimilar to that described above with respect to provisioning of a newlight path. However, according to particular embodiments, the flow ofrestoration path messages propagates in reverse along available routesfrom node A to node B. For example, node B may determine all availablelight paths from node A and, for each available light path, generate arecovery path message that indicates drop power level variation withinnode B for the wavelength associated with the light path. As withpreviously discussed messages, each node 12 along the route of a lightpath supplements the included power level variation with appropriatevalues. Thus, node A may perform restoration by selecting among anynumber of potential light paths based on aggregate power levelvariations for the light paths.

[0035] While the preceding descriptions and examples focus on particularembodiments for provisioning, protection, and restoration of lightpaths, system 10 contemplates nodes 12 using any suitable techniques foraggregating power level variations along light paths to select betweenand/or configure for communication on a light path.

[0036]FIG. 2 is a block diagram illustrating exemplary functionalcomponents of node 12, which includes a pre-amplifier 30, ade-multiplexer 32, an optical cross-connect fabric 34, a multiplexer 36and a post-amplifier 38. In addition, node 12 includes a controller 40and a memory 42 maintaining power level information that includes adddata 44, through data 46, and drop data 48. Node 12 also includesspectrum analyzer units (SAUs) 62 and power monitors 64 for use inmeasuring power level variations along various channels and routes. Ingeneral, node 12 supports power level management of opticalcommunications using power level information stored in add data 44,through data 46, and drop data 48. More specifically, node 12 exchangesinformation with other nodes 12 to permit selection, provisioning, andconfiguration of light paths based on aggregate power level variationscalculated across light paths.

[0037] In the embodiment illustrated, node 12 provides a number ofinputs and outputs. These include an input fiber 50 and an output fiber52 that couple node 12 to other nodes 12 within network 14. Node 12 alsoincludes drop fiber 54 and add fiber 56 that couple to othercommunications equipment, such as devices 16. In addition, node 12includes a control line 60 for exchanging management messages with othercommunications equipment, such as other nodes 12 and devices 16.However, while control line 60 is illustrated as a distinct input/outputline, management communications may take place between node 12 and otherequipment through any appropriate inputs and outputs, such as an opticalsupervisory channel (OSC). Moreover, while input fiber 50 and outputfiber 52 are described as coupling to other nodes 12 and drop fiber 54and add fiber 56 are described as coupling to other communicationsequipment, system 10 contemplates node 12 coupling various opticalinputs and outputs to any other appropriate optical communicationsequipment. For example, add fiber 56 may receive input generated andcommunicated along output fiber 52 of another node 12.

[0038] Pre-amplifier 30, de-multiplexer 32, optical cross-connect fabric34, multiplexer 36, and post-amplifier 38 represent traditionalcomponents for supporting optical communications. Using input fiber 50,node 12 receives optical signals communicated on any number of differentwavelengths. Each of these received signals may be passed through node12 and retransmitted on output fiber 52 or “dropped” and transmitted ondrop fiber 54. Node 12 may also receive one or more optical signals atvarious wavelengths using add fiber 56. Node 12 may introduce thesesignals into the traffic of network 14 by transmitting the signals onoutput fiber 52.

[0039] In the embodiment illustrated, the table within memory 42 thatmaintains add data 44, through data 46, and drop data 48 is expanded.This demonstrates a potential technique for maintaining power levelvariations for adding, dropping, and passing through optical signals ata number of different wavelengths. Add data 44 maintains power levelvariations for optical signals received on add fiber 56 and transmittedon output fiber 52. For each wavelength, this power level variationbetween signals received on add fiber 56 and signals transmitted onoutput fiber 52 represents the add power level variation. According toparticular embodiments, add power level variation is defined as thepower variation from the output of a transmitter coupled to add fiber 56to the input of post-amplifier 38. The add power level variation may bemeasured for each of the wavelengths serviced by node 12. Thus, forexample, if node 12 provides N wavelengths for the transmission ofsignals, node 12 may measure N add power level variations. Node 12maintains values for each of these power level variations within adddata 44.

[0040] To measure add power level variations, node 12 may communicatewith neighboring communications equipment, such as other nodes 12 and/ordevices 16. For example, node 12 may link to the output of device 16using add fiber 56. Using an OSC, node 12 may exchange information withdevice 16 to determine the power level variation that occurs across addfiber 56. Node 12 sums this value with variations due to internaloperations to determine an add power level variation. Thus, the addpower level variation will reflect power level variation from the outputof device 16 to the input of post-amplifier 38. To populate the tablewith add data 44, node 12 cycles through each channel, measuring the addpower level variation and recording this value within add data 44.However, node 12 may determine each value at any appropriate time ortimes.

[0041] Similar to measurements for add power level variations, throughpower level variations and drop power level variations may be measuredfor other paths through node 12. Through data 46 reflects the measuredpower level variations at the various wavelengths serviced by node 12between signals received on input fiber 50 and transmitted on outputfiber 52. Likewise, drop data 48 maintains measured power levelvariations at each wavelength serviced by node 12 between signalsreceived on input fiber 50 and transmitted on drop fiber 54. Accordingto particular embodiments, through power level variation is defined aspower variation measured along a particular channel between an outputcoupled to input fiber 50 and the input of post-amplifier 38. Similarly,drop power level variation is defined as the power level variation on aparticular channel between the output of pre-amplifier 30 and the inputof a receiver coupled to drop line 54.

[0042] To measure through and drop power level variations, node 12 usestechniques similar to those described above with respect to measurementsof add power level variations. For example, using communications withneighboring network equipment, node 12 can develop the entries in thetable that reflect add, drop, and through power level variations foreach wavelength serviced by node 12. Therefore, add data 44, throughdata 46 and drop data 48 maintain power level variations for thedifferent pathways for optical signals passing through node 12.

[0043] However, while specific definitions for add, through, and droppower level variations are described above, system 10 contemplates usingany appropriate definitions for add, through, and drop power levelvariations based upon appropriately designated beginning and end points,so long as those definitions permit the aggregation of power levelvariations along light paths. Moreover, system 10 contemplates node 12determining and/or updating power level information at any appropriatetimes using any suitable techniques. According to particularembodiments, node 12 uses spectrum analyzer units 62 and power monitors64 to periodically, sporadically, and/or continuously monitor powerlevel variations for adding, dropping, and passing through opticalsignals.

[0044] Controller 40 represents any suitable processor, controller,and/or suitable logic device for communicating power level informationwith other nodes 12 to enable power level management using aggregatepower level variations along light paths. In the embodiment illustrated,controller 40 links to other communications equipment using control line60. Through control line 60, controller 40 may exchange managementmessages, such as MPLS messages, with other communications equipment,such as other nodes 12. For example, through control line 60, controller40 can exchange various messages with other nodes 12 to support thecalculation of aggregate power level variations along light paths.However, as previously discussed, nodes 12 may use any suitable links toexchange management messages. For example, nodes 12 may use in-bandsignaling along communication channels, an optical supervisory channel(OSC), or any other appropriate link to exchange management messages.

[0045] In operation node 12 may function simultaneously as an add node,through node and/or drop node for one or more light paths. As an addnode, node 12 may initiate path setup messages and use responses toselect light paths and configure for operation. As a through node, node12 responds to various messages, sharing through data 46 to aid inestablishment of light paths. As a drop node, node 12 responds to pathsetup messages by sharing drop data 48 in responses. Moreover, as a dropnode, node 12 may also monitor active light paths and manage protectionand/or restoration in the event of failures. Thus, power levelinformation stored in Memory 42 represents an important functionalaspect of node 12, whether operating as an add node, through node,and/or drop node.

[0046] While the embodiments illustrated and the preceding descriptionfocus on a particular embodiment of node 12 that includes specificelements, system 10 contemplates node 12 having any suitable combinationand arrangement of elements for sharing power variation information toenable power level management of light paths using aggregate power levelvariations. Thus, the modules and functionalities described may becombined, separated, or otherwise distributed among any suitablefunctional components, and some or all of the functionalities of node 12may be performed by logic encoded in media, such as software and/orprogrammed logic devices.

[0047]FIG. 3 is a diagram illustrating exemplary values for power levelvariations along two potential light paths from a first node 12 (node L)to a second node 12 (node M). Along each light path, exemplary valuesare given for add, through, and drop power level variations at eachappropriate step. In addition, values for variations across connectingfiber segments are also provided (transmission power level variations).Thus, in this example, add, drop, and through values represent internalvalues that may be supplemented by the values for transmission powerlevel variations. In the embodiment illustrated, light path 1 and lightpath 2 represent two potential light paths between node L and node M.Each of these light paths pass through a number of intermediate nodes12, including node N, which is common to both light paths. At node N,light path 1 is routed through an add fiber, while light path 2 isrouted through node N, thus, the values provided for power levelvariations along each light path reflect these routes.

[0048] To determine the aggregate power level variations for each lightpath, nodes 12 may use techniques such as those discussed above. Forexample, node L may communicate a path setup message along each of lightpath 1 and light path 2, with each message accumulating values for powerlevel variations as it propagates along a light path. Thus, theaggregate power level variation for each light path will reflect add,through, drop, and transmission power level variations for appropriatenodes 12 and traversed fibers.

[0049] Using replies reporting these aggregate power level variations,node L may select and configure to provide suitable signals forreception by node M. For example, given the values provided in thisillustration and assuming an algorithm that selects the smallest powerlevel variation, node L will select light path 1. However, as previouslydiscussed, system 10 contemplates nodes 12 using any suitable techniquesfor determining aggregate power level values and selecting betweenpotential light paths based upon these values. Moreover, the exampleillustrated and accompanying description are provided only to clarifythe operation of a particular embodiment.

[0050]FIG. 4 is a flowchart illustrating a method for node 12 todetermine and use aggregate power level variations for potential lightpaths to a remote node 12. Node 12 receives a request to establish anoptical path to a remote drop node 12 at step 100. Node 12 then, atsteps 102 to 112, identifies potential light paths and initiates thedetermination of aggregate power level variations on these light paths.Node 12 determines an available light path to the drop node at step 102and reserves the resource to the next node 12 for the light path at step104. For example, node A may identify an available light path to node Bthat passes through node C and reserve the channel on the fiber segmentfrom node A to node C. By reserving the resource, node A ensures thatthe potential channel will remain available until a decision is madewhether or not to use the associated light path.

[0051] Node 12 determines the add power level variation for the lightpath at step 106. For example, node 12 may access add data 44 storedwithin memory 42 to determine the add power level variation for thechannel associated with the light path. Node 12 then generates a pathsetup message indicating the determined add power level variation atstep 108 and communicates the message to the next node 12 for the lightpath at step 110. For example, as previously discussed, node A maygenerate an MPLS message incorporating the add power level variation andcommunicate the message to node C.

[0052] Node 12 determines whether all available light paths to the dropnode 12 have been identified at step 112. If not, node 12 continues toidentify available light paths and generate path setup messages forthese light paths. Thus, in the embodiment illustrated in thisflowchart, node 12 can potentially identify all light paths availablefor establishing an optical communication link with drop node 12.However, system 10 contemplates node 12 using any suitable algorithmsfor limiting the light paths selected for consideration. For example,according to particular embodiments, nodes 12 each maintain informationdetailing topography of some or all of network 14 and use thisinformation to identify potential routes between nodes 12.

[0053] At steps 114 to 128, node 12 receives and processes replies topath setup messages. Thus, node 12 determines whether a reply to a setupmessage has been received at step 114. If so, node 12 determines whetherthe reply indicates unavailability of the light path indicated in thepath setup message. For example, while a particular channel may beavailable between node A and node C for a light path, node C maydetermine that a corresponding channel between node C and node F isunavailable. In response, node C may inform node A of the unavailabilityof the light path. In response to a reply indicating light pathunavailability, node 12 releases the reserved resource at step 118.Thus, since the resource to the next node 12 will not be used for thiscommunications link, node 12 can release the reservation so that theresource may be used for other links.

[0054] If the reply does not indicate unavailability of the light path,then the reply indicates an aggregate power level variation for thelight path. Using the aggregate power level variation in the reply, node12 determines an appropriate configuration. For example, node 12 maydetermine the power level and/or variable attenuation settings thataccommodate for the indicated aggregate power level variation to providesuitable signals for reception by drop node 12. If the determinedsettings are not within the range of node 12, then node 12 will not usethis light path. Thus, if the settings are out of range, node 12 willrelease the resource reserved for this light path at step 118. Inaddition, node 12 may inform intermediate nodes 12 to release anyreserved resources for the light path.

[0055] However, if the settings are within range, node 12 determineswhether the setting are the most favorable calculated at step 124. Inthis process, node 12 attempts to identify the most favorable light pathbased upon aggregate power level variations and/or determinedconfigurations. As previously discussed, node 12 may use any suitablealgorithms, target values, and/or calculations to determine whether onelight path is more favorable than another. If the light path is not themost favorable, node 12 releases the resource at step 118 and, inaddition, may inform intermediate nodes 12 to release correspondingresources. However, if the light path is the most favorable, node 12selects the light path as the current selection at step 126. Node 12continues this process until replies to all path setup messages havebeen received (or some other suitable event, such as a time out). Thus,node 12 determines whether additional replies remain outstanding at step128 and, if so, continues monitoring for replies at step 114.

[0056] Upon receiving all appropriate replies, node 12 determineswhether a light path has been selected at step 130. This determineswhether one of the potential light paths identified was available andhad an aggregate power level variation indicating settings within therange of node 12. If not, node 12 may report an error at step 132. Forexample, node 12 may generate an error message and communicate themessage to the device that requested the optical communication link.However, if a light path has been selected, node 12 ensures that allunused resources are released at step 134 (including notifyingintermediate nodes 12 to release unused resources). Node 12 configuresfor the selected light path at step 136. For example, node 12 mayconfigure components to provide the power levels and/or variableattenuations determined for the selected light path. Node 12 thenestablishes communications on the selected light path at step 138.

[0057] The preceding flowchart illustrates only an exemplary method ofoperation, and system 10 contemplates nodes 12 using any suitabletechniques and elements for identifying potential light paths and usingpower level variation information received from other nodes 12 to selecta light path for communication. Thus, many of the steps in thisflowchart may take place simultaneously and/or in different orders thanas shown. In addition, node 12 may use methods with additional steps,fewer steps, and/or different steps, so long as the methods remainappropriate.

[0058]FIG. 5 is a flowchart illustrating a method for node 12 to sharepower level information with other nodes 12. Thus, this flowchartdetails the operation of node 12 as a potential intermediate node of alight path. Node 12 monitors received management messages at step 150.For example, node 12 may monitor MPLS messages received from other nodes12 using control line 60. In this flowchart, the method providesprocessing for path setup messages and replies indicating failure toestablish a light path. Node 12 determines whether a setup failure replyhas been received at step 152. Node 12 may receive this reply in avariety of scenarios. For example, node C may, after receiving a pathsetup message from node A, communicate a similar path setup message tonode F. If node F determines that no corresponding channel is availablebetween node F and node I, node F may communicate a setup failuremessage to node C. Node C may also receive setup failure messages fromnode A. For example, upon determining not to use a particular light paththrough node C, node A may inform node C of the failure.

[0059] In response to receiving a setup failure reply, node 12 releasesany reserved resources at step 154. In addition, node 12 communicatesthe setup failure message to the previous node 12 in the light path atstep 156. (Or communicates the setup failure message to the next node 12in the light path as appropriate.) This permits all nodes 12 to releasereserved resources when appropriate.

[0060] In response to detecting a path setup message at step 158, node12 determines whether the next segment for the indicated light path isavailable at step 160. For example, upon receiving a path setup messagefrom node A indicating a particular channel, node C may determinewhether a corresponding channel is available on the fiber between node Cand node F. If node 12 determines that the next segment for theindicated light path is unavailable, node 12 communicates a setupfailure message to the previous node in the light path at step 156.However, if the segment is available, node 12 reserves the resource atstep 162.

[0061] Node 12 also determines through power level variation for thechannel indicated in the path setup message at step 164. For example,node 12 may access through data 46 maintained in memory 42 to determinethe value indicated for the particular channel. Node 12 adds this valueto the power level variation indicated in the path setup message at step166. Therefore, the value indicated in the path setup message willreflect the aggregate power level variation up to and through thecurrent node 12. Node 12 communicates the path setup message to the nextnode 12 in the light path at step 168. This technique permitsdistribution of processing and data maintenance that providesscalability while retaining network level power level management.

[0062] However, as with the earlier described flowchart, the precedingflowchart illustrates only an exemplary method of operation. Thus, manyof the steps in this flowchart may take place simultaneously and/or indifferent orders than as shown. In addition, node 12 may use methodswith additional steps, fewer step, and/or different steps, so long asthe methods remain appropriate.

[0063]FIG. 6 is a flowchart illustrating a method for node 12 todetermine and share power level variations for power level management oflight paths across network 14. This flowchart focuses in particular uponthe operation of node 12 as a drop node for a communication path. Node12 monitors received management messages at step 200 to determinewhether a path setup message has been received at step 202. Uponreceiving a path setup message indicating node 12 as a drop node, node12 determines drop power level variation for the indicated light path atstep 204. For example, node 12 may access drop data 48 maintained inmemory 42 to determine a value for drop power level variation on thechannel identified within the path setup message. Node 12 adds the droppower level variation to the aggregate power variation value indicatedin the path setup message at step 206. Thus, at this point, node 12 hasdetermined the aggregate power level variation for the entire light pathfrom the originating add node 12 to drop node 12. Node 12 generates areply indicating this aggregate power level variation at step 208 andcommunicates the reply message to add node 12 at step 210.

[0064] However, as with the earlier described flowcharts, the precedingflowchart illustrates only an exemplary method of operation. Thus, manyof the steps in this flowchart may take place simultaneously and/or indifferent orders than as shown. In addition, node 12 may use methodswith additional steps, fewer step, and/or different steps, so long asthe methods remain appropriate.

[0065]FIG. 7 is a flowchart illustrating the operation of node 12 inmonitoring for and responding to failure of a light path. The chartfocuses in particular upon the operation of node 12 operating as a dropnode. Node 12 monitors active light paths at step 220. For example, aspreviously discussed, node 12 may monitor for the continuous receipt oflight along each light path currently in use. Upon detecting a failureof a light path at step 222, node 12 initiates messaging to reestablishthe communication link while further providing power level managementfor the backup/protection light path.

[0066] In the embodiment illustrated by this flowchart, node 12 attemptsto reestablish the communication link using a dedicated protection lightpath. Node 12 determines a drop power level variation for the protectionlight path at step 224. Node 12 generates a protection path setupmessage indicating the determined drop power level variation at step 226and communicates the setup message to the previous node 12 in theprotection light path at step 228. As previously discussed, this messagethen propagates in reverse along the light path accumulating power levelvariations along the way. Thus, this message eventually provides noticeto the originating add node 12 of the failure while further providinginformation suitable for reestablishing the communication link on theprotection light path with appropriate configurations.

[0067] The preceding flowcharts and accompanying description illustrateonly exemplary methods of operation, and system 10 contemplates nodes 12using any suitable techniques and elements for operating as add nodes,drop nodes and through nodes. Thus, many of the steps in theseflowcharts may take place simultaneously and/or in different orders thanas shown. For example, since each node 12 may simultaneously operate asan add node, drop node, and/or through node, a single node 12 maysimultaneously perform many of the techniques illustrated by theseflowcharts. In addition, nodes 12 may use methods with additional steps,fewer steps, and/or different steps, so long as the methods remainappropriate.

[0068] Although the present invention has been described in severalembodiments, a myriad of changes and modifications may be suggested toone skilled in the art, and it is intended that the present inventionencompass such changes and modifications as fall within the scope of thepresent appended claims.

What is claimed:
 1. A method for power level management of opticalcommunications, the method comprising: receiving a path setup messageidentifying a light path between an add node and a drop node, the pathsetup message comprising a power level variation value; determiningwhether a channel for the light path to a next node in the light path isavailable; and if the channel is available: determining through powerlevel variation for the light path; adding the through power levelvariation to the power level variation value in the path setup message;and communicating the path setup message to the next node in the lightpath.
 2. The method of claim 1, further comprising, if the channel isnot available, communicating a path setup failure message to a previousnode in the light path.
 3. The method of claim 1, further comprisingmaintaining through data indicating a through power level variation foreach of a plurality of channels.
 4. The method of claim 1, furthercomprising reserving the channel to the next node for the light path. 5.The method of claim 4, further comprising: receiving a path setupfailure message from the next node, the path setup failure messageidentifying the light path; and in response to the path setup failuremessage, releasing the channel reserved for the light path.
 6. Themethod of claim 5, further comprising communicating the path setupfailure message to a previous node on the light path.
 7. An opticalcommunication node comprising: a cross-connect fabric operable toreceive optical communications from an input fiber and an add fiber andto switch received optical communications for transmission on a selectedone of an output fiber and a drop fiber; and a controller operable toreceive a path setup message identifying a light path between an addnode and a drop node, the path setup message comprising a power levelvariation value. and to determine whether a channel for the light pathto a next node in the light path is available, the controller furtheroperable, if the channel is available, to determine through power levelvariation for the light path, to add the through power level variationto the power level variation value in the path setup message, and tocommunicate the path setup message to the next node in the light path.8. The node of claim 7, further comprising: a first optical amplifiercoupled to the cross-connect fabric and operable to receive opticalcommunications from the input fiber; and a second optical amplifiercoupled to the cross-connect fabric and operable to transmit opticalcommunications on the output fiber.
 9. The node of claim 8, furthercomprising a memory maintaining through data indicating a through powerlevel variation for each of a plurality of channels.
 10. The node ofclaim 9, wherein the through power level variation for a selected one ofthe channels indicates variation in power between an output of a devicecoupled to the input fiber and the second optical amplifier at awavelength of the selected channel.
 11. The node of claim 7, wherein thecontroller is further operable, if the channel is not available, tocommunicate a path setup failure message to a previous node in the lightpath.
 12. The node of claim 7, wherein the controller is furtheroperable to reserve the channel to the next node for the light path. 13.The node of claim 12, wherein the controller is further operable to:receive a path setup failure message from the next node, the path setupfailure message identifying the light path; and in response to the pathsetup failure message, release the channel reserved for the light path.14. The node of claim 13, wherein the controller is further operable tocommunicate the path setup failure message to a previous node on thelight path.
 15. Logic for power level management of opticalcommunications, the logic encoded in a medium and operable when executedto: receive a path setup message identifying a light path between an addnode and a drop node, the path setup message comprising a power levelvariation value; determine whether a channel for the light path to anext node in the light path is available; and if the channel isavailable: determine through power level variation for the light path;add the through power level variation to the power level variation valuein the path setup message; and communicate the path setup message to thenext node in the light path.
 16. The logic of claim 15, furtheroperable, if the channel is not available, to communicate a path setupfailure message to a previous node in the light path.
 17. The logic ofclaim 15, further operable to maintain through data indicating a throughpower level variation for each of a plurality of channels.
 18. The logicof claim 15, further operable to reserve the channel to the next nodefor the light path.
 19. The logic of claim 18, further operable to:receive a path setup failure message from the next node, the path setupfailure message identifying the light path; and in response to the pathsetup failure message, release the channel reserved for the light path.20. The logic of claim 19, further operable to communicate the pathsetup failure message to a previous node on the light path.
 21. Anoptical communication node comprising: means for receiving a path setupmessage identifying a light path between an add node and a drop node,the path setup message comprising a power level variation value; meansfor determining whether a channel for the light path to a next node inthe light path is available; and means for, if the channel is available:determining through power level variation for the light path; adding thethrough power level variation to the power level variation value in thepath setup message; and communicating the path setup message to the nextnode in the light path.